Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$170.47	11.351%	$189.82	$189.82	$189.80	$189.80
Purchase #2	$162.90	4.510%	$170.2468	$170.25	$170.25	$170.20
Purchase #3	$156.54	13.734%	$178.0392	$178.04	$178.05	$178.00
Purchase #4	$176.47	7.642%	$189.9558	$189.96	$189.95	$190.00
Purchase #5	$33.33	13.501%	$37.8299	$37.83	$37.85	$37.80
Purchase #6	$29.33	12.861%	$33.1021	$33.10	$33.10	$33.10
Purchase #7	$39.69	7.283%	$42.5806	$42.58	$42.60	$42.60
7 purchase totals =	$768.73		$841.5744	$841.58	$841.60	$841.50